The present invention relates to displacement sensors for servo-control actuators.
Linear variable differential transducers (LVDTs) are conventionally used as sensors for servo-control actuators, and in particular in the aviation field for flight control actuators.
As shown in FIG. 1, such a displacement sensor usually comprises a sensor body 1 which is fixed on one end of the cylinder 2 of the actuator and which extends lengthwise relative to said actuator.
One or more coils are placed in conventional manner inside the body 1.
A core-forming plunger 4 is slidably mounted in the body 1 and extends in the rod 3 of the actuator beyond said body 1, being fixed on an endpiece 5 that terminates said rod 3. This endpiece is generally constituted by a connection piece having the hinge of the actuator mounted thereon.
It is necessary for such a displacement sensor to be capable of being adjusted, particularly when the actuator is being installed, e.g. on an aircraft, or else during operation of the actuator, in order to take account of any drift in the actuator or the sensor.
For this purpose, structures are already known in which the core 4 of the sensor is fixed on the endpiece 5 which terminates the rod 3 of the actuator by cooperation between an outside thread on the core 4 and an inside thread of the endpiece 5.
Adjustment means enable the core 4 to be rotated so as to adjust the depth with which it is engaged in the endpiece 5.
In known structures, the adjustment means are constituted by a knurled knob which meshes with the thread of the core 4.
For this purpose, a recess is provided in the connection piece at the endpiece 5, which recess passes through the thickness of the connection piece and receives the knob.
Such a structure presents several drawbacks.
In particular, it makes it necessary to provide a recess for receiving the knob in a portion of the connection piece of the hinged link which terminates the endpiece, i.e. in a part which is subject to high levels of stress.
This weakens the connection piece of the hinge, thereby making it necessary to increase the size of the connection piece.
Furthermore, the above-mentioned known structures do not enable very great accuracy to be obtained when adjusting the sensor.
Objects of the invention are to mitigate those drawbacks.
The invention proposes a structure comprising firstly a differential sensor of linear displacement comprising a body and a core slidably mounted relative to said body, and secondly a rod of a servo-control actuator in which the core is mounted, said rod terminating in an endpiece which has a bore in which the core is received close to its end, said bore and the core having complementary threads which co-operate to hold said core relative to said bore, and means enabling the engagement of the core in said bore to be adjusted, wherein said means comprise an adjustment screw extending through the actuator rod and whose thread co-operates with complementary means carried by the core so that turning movement applied to the adjustment screw by an operator gives rise to axial displacement of the core in the bore of the endpiece.
The invention is advantageously associated with the various following characteristics taken singly or in any feasible combination:
the said adjustment screw extends through the actuator rod perpendicularly to the plane of a connection piece of a hinge which terminates the endpiece of the actuator rod;
the complementary means with which the thread of the adjustment screw co-operates is constituted by fluting extending a portion of the core;
the structure includes a locking screw which extends parallel to the adjustment screw and which presents a projection in the vicinity of its head, the projection extending perpendicularly to said adjustment screw and being designed to engage in a slot in the head of said adjustment screw to lock said screw in a given position;
the adjustment screw has a single diametral slot or it has a cross-shaped slot; and
the core has a guiding bearing surface between its fluted portion and a threaded portion whose thread cooperates with the thread of the bore of the endpiece.
The invention also proposes a servo-control actuator and in particular an aircraft flight control actuator, the actuator including a structure of the above-specified type.